What Is El Niño?

The Short Answer:

El Niño is a weather pattern that occurs in the Pacific Ocean. During this time, unusual winds cause warm surface water from the equator to move east, toward Central and South America. El Niño can cause more rain than usual in South and Central America and in the United States.

Cartoon boy with umbrella in a rain storm says Sweet! Another El Niño.

Credit: NOAA/JPL-Caltech

El Niño is a weather pattern that occurs in the Pacific Ocean, but it is so big that it affects weather all over the world.

Weather depends a lot on ocean temperatures. Where the ocean is warm, more clouds form, and more rain falls in that part of the world. In the Pacific Ocean, near the equator, the Sun makes the water especially warm on the surface.

Normally, strong winds along the equator push the warm surface water near South America westward toward Indonesia. When this happens, the cooler water underneath rises up toward the surface of the ocean near South America.

Map shows conditions in a normal year, with trade winds blowing west across the Pacific at the equator, pushing warm surface water toward Indonesia.

Credit: NOAA/JPL-Caltech

However, in the fall and winter of some years, these winds are much weaker than usual. They actually blow the other way (toward South America instead of Indonesia) in October. So the warm surface water along the equator piles up along the coast of South America and then moves north towards California and south toward Chile.

Map shows conditions in an el Niño year, the trade winds weaker, allowing warm surface water in the Pacific to pile up off the west coast of South America.

Credit: NOAA/JPL-Caltech

Many fish that live in the normally cooler waters off the coast of South America move away or die. Fishermen first called this condition of warm coastal water and poor fishing "El Niño." El Niño means "the Christ Child." They call it that because it typically occurs at Christmastime.

In El Niño years, lots of rain clouds form over this warm part of the ocean. These clouds move inland and dump much more rain than usual in South and Central America and in the United States.

3-D cloud and surface temperature data are combined in this image, which shows a well-developed El Niño condition.

3-D cloud and surface temperature data are combined in this image from the Terra satellite, which shows a well-developed El Niño condition. The red area is warm water sitting off the coast of western South America.

Meanwhile, other parts of the world can suffer drought. Weather patterns all over the world may be unusual, making lakes out of deserts and charcoal heaps out of rain forests.

How do you take the ocean's temperature from space?

How do we know what is happening to the ocean temperatures around the Earth? One way is to use data from weather satellites in space.

Satellite image shows warmer than average waters in the Pacific during February 2015.

El Niño arrives in 2015. This image shows the temperature of the ocean's surface during February 2015. The measurements were made by NOAA satellites. The large area of red shows warmer than average waters in the Pacific Ocean near the equator. This warmer water creates a weak El Niño condition. Credit: NOAA

One of the jobs of the GOES-16 satellite is to measure the temperature of the ocean's surface. Scientists use data from GOES-R series satellites--along with data from the MODIS (or Moderate Resolution Imaging and Spectroradiometer) instrument on NASA's Terra and Aqua satellites--to study cloud properties, land surface properties, sea surface temperature, fires, volcanic ash, snow cover, and sea and lake ice.

This information about sea surface temperature can allow scientists to more accurately detect conditions such as El Niño while they are forming.